1. Calculating Degree Days Ashley Font National Science Foundation Graduate STEM Fellow in K-12 Education Sugar Creek Watershed K-12 Education Program The Ohio State University-Ohio Agricultural Research and Development Center

2. The Degree Day  FIRST OF ALL! Degree DAY is not a literal DAY  It is just CALLED a Degree DAY

3. The Degree Day  Unit of Heat  Average amount of heat in degrees that have occurred in a single day  1 Degree Day results when the Average daily temperature is 1 degree above the lower threshold EX: Average 51 degrees, threshold is 50 degrees… 51-50= 1 dd

4. What is a lower threshold?  Just means the lowest temperature that something can grow at.  Some insects cannot develop until the temperature is 50°F Any lower, and the bug stops growing!  Therefore, 50°F would be that bug’s threshold

5. Why do we use it?  Monitoring these values of heat can help us predict pest activity  Since insects are cold blooded, daily temperatures have A LOT to do with their development  Temperature can be more precise than just using calendar dates.

6. Calculations  Use the daily maximum temperature and the daily minimum temperature  Get an Average for the day  Subtract a lower threshold (we use 50F unless otherwise instructed)

7. The Formula (Max. Daily Temp. + Min. Daily Temp.) __ Lower 2 Threshold

8. Examples (pg 2) #1 June 1st, 2008 MAX: 74.1°F MIN: 50.2°F Lower Threshold: 50°F Calculation (74.1 + 50.2 ) - 50 = 12.15 2  So, on June 1st, 12.15 Degree Days have accumulated

9. Examples cont. (pg 2) # 2  When the minimum daily temperature is BELOW the lower threshold, REPLACE the Minimum Daily Temp in the formula with the THRESHOLD.**  May 28th,2008  MAX: 66.5°F MIN: 38.6°F LT: 50°F ( 66.5 + 50 ) - 50 = 8.25 2

10. Examples cont. (pg 2) #3 ** There are not NEGATIVE degree days. If the formula results in a negative, it is ZERO degree days… meaning no heat accumulated on this day January 1 st Max:41.6 Min:19.0 LT: 50°F (41.6 + 50) - 50 = -4.2 2  So, ZERO DD.  No development occurred this day.

11. Cumulative Degree Day  Just adding up each day’s DD units to get the total for multiple days  Usually start adding at January 1 st.  This can help us predict what day of the year something will occur by following how much heat is accumulated each day.

13. Assignments  Do in class  In pairs  Use Calculators